Of the nine kids born to Richard and Judy Perry of Freeland Street, everyone agrees that the family favorite was Dennis.

Gentle, happy and childlike, Dennis was born with a developmental disability and had an IQ of 40. But what he lacked in intellect he made up for with an infectious enthusiasm for just about everything — sports, animals, the Beach Boys, travel and family softball games that typically featured a beaming Dennis batting for both sides.

"Dennis was the life of the party," said his sister Nancy Perry Mias. "Everyone was drawn to him. He was so easy to please, and you just wanted to do things for him."

But Dennis was largely self-sufficient. As a teen he had become one of the first residents of the Templeton Developmental Center, a state-run facility for the mentally handicapped set on a bucolic 1,600 acres. Dennis would live there for more than 40 years; he adored his adopted home and took special pride in caring for the cows in the dairy barn.

On Sept. 16, his sister Nancy received a phone call from a nurse at the center. Dennis had fallen in the barn, hit his head and was on his way to Henry Heywood Hospital in Gardner. As Nancy raced to the hospital she received a second call, saying he was being airlifted to UMass Memorial Medical Center.

Dennis Perry spent 12 days in an induced coma at UMass before he died Sept. 27. He was 64. Just as his devastated family reeled from the loss, they received another unthinkable shock: Their brother's fall was no accident.

Three weeks after Perry was injured, state police arrested a 22-year-old resident of the Templeton Developmental Center on charges that he deliberately shoved him into a boiler in the barn. Two staff members witnessed the incident and told police that the attack was unprovoked.

Some would also argue that it was not unexpected. The alleged assailant, Anthony Remillard of Worcester, was a volatile man with a significant criminal history. He had been sent to Templeton over the objections of prosecutors who had requested he go to Bridgewater or Worcester State Hospital. Instead, he was allowed to enter Templeton in August 2012, while awaiting trial on arson charges.

But a Worcester Superior Court judge set conditions, one of which was that any incidents involving Remillard be reported to the court. Eight months before he shoved Perry in the barn, Remillard allegedly punched a staffer in the chest and had to be restrained. Templeton never reported the incident, investigators said.

"My concern is that a man is dead, and there were things that were supposed to happen that could have prevented this, and they didn't happen," District Attorney Joseph Early said last week.

Likewise, family members and advocates for the mentally ill demand to know why a man with a history of violence was placed with residents as gentle and innocent as Dennis Perry. The center has been slated to close for years, and while Perry was moved to a group home in Athol a year before his death, he still spent his days at Templeton.

Attorney Thomas Frain of Bolton, who specializes in cases involving developmentally disabled people, noted that the state is moving to privatize intermediate care facilities such as Templeton and that they don't accept many new clients, so most of the current residents are elderly.

"This population is old, frail and medically needy," he said. "Why were they holding someone violent and dangerous with a docile 64-year-old man? Someone is dead for no apparent reason. If you're going to take someone like that, you have an obligation to keep everyone safe. I think they should answer for what happened there."

But answers were hard to come by last week. Patricia Lyons, director of the Templeton facility, did not return phone calls. And questions put to Alec Loftus, spokesman for the Executive Office of Health and Human Services, weren't answered in a brief email that referred questions to Early's office.

"In response to your basic questions about admission criteria and policies at Templeton Developmental Center, all individuals referred to TDC for admission must be eligible for supports by the Department of Developmental Services," Loftus wrote. "Staffing and clinical services are individualized for each person and DDS works to promote the health and safety of all residents."

Remillard, who had lived with his mother at 57 Lafayette St., was developmentally disabled and repeatedly found not competent to stand trial in previous criminal cases, according to court records. He had three cases pending before his admission to Templeton. His history includes charges that he hit his 12-year-old brother in the face with a baseball bat in May 2011, and that four months later he pulled a knife on someone and punched him in the face.

In May 2012, he allegedly set fire to a building at 50 Lafayette St., near his home. In June of that year he was admitted to Westwood Lodge due to a "psychotic break," and he cut off a GPS bracelet. In August, after Worcester State Hospital refused to accept Remillard because of the arson charge, he was sent by a judge to Templeton.

Remillard's treatment plan by DDS required that he be monitored by staff at all times except when in his room with his door alarm on, according to papers filed with the state Trial Court.

"A focus will be on treating others respectfully and accepting responsibility for his actions," the DDS treatment plan says.

The treatment plan failed, and so did administrators at Templeton. Not only did they neglect to report that Remillard allegedly assaulted a staffer, but they never reported the fatal attack on Dennis Perry. Instead, investigators learned of it from the medical examiner.

When state police went to arrest Remillard on Oct. 2 — three weeks after the alleged assault — they found him still living at the Templeton Developmental Center. And the Perry family only learned of the arrest in the newspaper.

Today, his siblings say they never would have allowed their brother to remain in a facility that housed violent criminals. They're saddened that such a senseless tragedy unfolded in the place he loved. And they can't imagine future gatherings without Dennis, the family favorite, who loved to buy them gifts with money he earned in the dairy barn.

"These people are the innocents of the world, and they need to be protected," said his sister Paula. "This didn't have to happen. ... People always said that Dennis was so lucky to have such a devoted family. But we were the lucky ones, to have Dennis for our brother."